Polymerization catalysts, such as Ziegler-Natta type catalysts, are usually deposited on solid carrier particles. The chemical composition, the structure of the surface, the morphology, and the size of the particles are important for the activity of the catalyst and for the properties of the polymer to be produced.
Certain carriers, such as MgCl2*(ROH)n, in which R is an alkyl group and n is 1 to 6, are prepared by melting the substance and then crystallizing the melt in a spraying chamber. The crystallized particles are screened in order to remove too small and too big particles. The melt may be sprayed e.g. through a rotating nozzle, as described in EP 655 073. One problem in such processes is that the carrier tends to stick and agglomerate on the walls of the chamber. This decreases the yield and quality of the carrier. Pneumatic hammers have been used for removing the carrier from the walls. This has, however, not been very effective. Hammering also easily damages the chamber.